Dimeric structures thallium compounds

Consequently, due to preferred cis-cis orientation a dimeric structure is observed for the indium complex and an unprecedented cis-trans arrangement in the thallium structure leads to a polymeric aggregate. Further N-NMR spectroscopic studies show that the aluminum and gallium complexes are stable contact ion pairs even in solution whereas the indium and thallium compounds are solvent-separated ion pairs in THE solution. 

The utility of thallium(III) salts as oxidants for nonaromatic unsaturated systems is a consequence of the thermal and solvolytic instability of mono-alkylthallium(III) compounds, which in turn is apparently dependent on two major factors, namely, the nature of the associated anion and the structure of the alkyl group. Compounds in which the anion is a good bidentate ligand are moderately stable, for example, alkylthallium dicar-boxylates 74, 75) or bis dithiocarbamates (76). Alkylthallium dihalides, on the other hand, are extremely unstable and generally decompose instantly. Methylthallium diacetate, for example, can readily be prepared by the exchange reaction shown in Eq. (11) it is reasonably stable in the solid state, but decomposes slowly in solution and rapidly on being heated [Eq. (23)]. Treatment with chloride ion results in the immediate formation of methyl chloride and thallium(I) chloride [Eq. (24)] (55). These facts can be accommodated on the basis that the dicarboxylates are dimeric while the... 

Tetraethylammoniumhis(tetracarbonyliron)bis(/i-tetracarbonyliron)dithal-late(2 — ), [Et4N]2[Tl2Fe4(CO)16], decomposes rapidly upon exposure to air and is soluble in MeOH, CH2C12, and most polar organic solvents. Its crystal structure shows it to be a weak dimer of [Tl Fe(CO)4 2] and it probably exists as the monomer in solution.15 IR (CH2C12, cm-1) 1985(m), and 1908(s). It may be oxidized or irradiated to yield higher nuclearity thallium-iron carbonyl compounds.14,15... 

Aluminum, gallium, indium, and thallium have been successfully incorporated in cyclic systems, although little structural information has been obtained (75). Hoberg (34) has prepared many such ring compounds, including, for example, 8a and 8b, and has demonstrated the former to be dimers from molecular mass determinations and from mass spectra. 

The structures of four tri-t-butoxysilanthiolates 210-213 have been reported. Whereas 210 is tetrameric with a nearly planar eight-membered ring, 211 and 212 are dimeric. In addition to the two thiolate S atoms the thallium atoms in 211 are also coordinated, albeit more weakly, by one butoxy O atom at a distance of 2.799(4) A. A similar (2+1) coordination is found for the mercury atoms in the monomeric species 212 [d(Hg-O) = 2.878(4) A]. Remarkably short Si-S distances are found in 213 and, in particular, 211 [2.078(2) A], suggesting that the M-S bonds (M = Pb, Tl) may exhibit a marked degree of ionicity in these compounds. 

Barbera et al. prepared a series of thallium(I) complexes, in which the position and number of side chains were changed systematically ((58) M = Tl). A minimum of four chains was required to induce mesomorphism in these systems (Table 37), and on the basis of X-ray diffraction, the monotropic mesophases were identified as Colii. The formation of the columns was due to the association of these half-disk compounds into dimers, and to their subsequent stacking. The dimeric nature of these thallium(I) complexes was confirmed by the analysis of the single-crystal structure of the non-mesomorphic dimethoxy analog. In the crystalline phase, the co-planar... 

Three other varieties of supramolecular self-assembly have been reported for cyclopentadienylthallium(I) compounds. Particularly remarkable is pentabenzylcy-clopentadienylthallium(I), 51, two modifications of which have been found, depending on the crystallization conditions. In the first modification, 51a, the crystal structure consists of covalent molecules which are associated to dimeric units by thallium-thallium interactions [48]. The second modification, 51b, forms pale yellow, needle-like crystals. In the crystal structure the molecules are associated as almost linear polymeric chains in which each thallium atom is effectively shielded by five benzyl groups [49],... 

No monomeric alkali metal alkyls or aryls are known, as those crystal structures which have been determined indicate electron-deficient, e.g. (MeLi), or ionic (K Me ) constitutions. The dialkyls of the lighter second group metals are mostly electron-deficient dimers or polymers, but those of zinc, cadmium and mercury are monomers with a linear structure as expected from participation of one (metal) s and one p orbital (with or without dji participation). In the third group the pattern is more complex. Whereas the trialkylboranes are monomeric, boron hydrides (and alkyl hydrides) and polyboron compounds form electron-deficient structures. Aluminium alkyls and alkyl hydrides are normally electron-deficient dimers or trimers gallium trialkyls are monomeric though the trivinyl is a dimer trimethylindium is a weakly associated tetramer in the solid state, otherwise all indium and thallium trialkyls appear to be monomers. 

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